Waterproof spark plug shield



Jan..l0, 1956 c. s. MARDEN 2,730,562

WATERPROOF SPARK PLUG SHIELD Filed Jan. 11, 1951 fzzverzor Cmrkdarz 5- Marafem United States Patent.

WATERPROOF SPARK PLUG SHIELD Carleton S. Marden, Waltham, Mass., assignor to National Products Corporation, Boston, Mass, a corporation of Massachusetts- Application January 11, 1951, Serial No. 205,561

6 Claims. (Cl. 174-35) This invention relates toa device for shielding the spark plug of an internal combustion engine and preventing electromagnetic radiation therefrom and particularly to a shield which also provides a watertight seal for the electrical connection between an ignition cable and the spark plug terminal.

The need for electromagnetic shielding has long been recognized in the internal combustion art and it has been customary to provide shielding by enclosing the spark plug in a metallic cover which is grounded to a cylinder block or like spark plug support. Such a cover, however, has the undesirable effect of producing excessive condensation and accumulation of foreign substances at the terminal post and insulator of the spark plug thereby grounding the high potential at the terminal and preventing combustion. If it is attempted to seal the chamber within the shield, particularly by atight metal to metal connection, the undesired condensation and accumulation is increased, since the metal parts will expand while the engine is heated, thus breaking the seal, then draw in moist and oily vapor as the engine cools, and thereafter seal the moisture and oil in the chamber about the spark plug.

A further objection to previous shields resides in the danger of their being loosened'by vibration. Owing to the weight of the shield the spark plug is more likely to become grounded or disconnected from the ignition cable than if no shield is used. However, previous attempts to lock the shield to the engine block have involved complicated mechanical connectionswhich hinder replacement or servicing of the spark plugs.

One object of the present invention, therefore, is to provide a mechanical connection by which the shield may be easily attached without the use of tools, and yet which will not loosen because of vibration.

Another object is to provide a shield which prevents the accumulation of moisture or other foreign matter on the terminal or insulator of the spark plug.

A further object is to provide a way of grounding the shield which does not obstruct access to the spark plug, and thus facilitates insertion and removal of the plug from the cylinder or other support.

Another object is to provide a waterproof spark plug shield of light construction which may be easily and inexpensively manufactured.

In one aspect the invention comprises a metallic cap member adapted to enclose and magnetically shield a spark plug, mounted within the cap member a hood of elastic insulating material having a sleeve portion for receiving and enclosing the binding post of the spark plug with substantially no air space thereabout and for resiliently gripping the spark plug, the hood being resiliently connected to the cap member so that the cap member is held about the hood, whereby the hood seals off the terminal and prevents the accumulation of moisture at the terminal, while the shield is mechanically connected or attached to the spark plug with a vibration-damping elastic connection. Preferably the hood member has a mounting portion integral with said sleeve portion joined to the cap member. The sleeve and mounting portions may be disposed coaxially or at an angle to each other so that the mounting member may extend respectively through the end or the side Wall of the hood.

One way of electrically connecting the shield to the spark plug receptacle is by means of a cup adapted to be fixed relatively to the spark plug support and to receive the shield telescopingly, the shield and cup making a yielding fit so that the amount which the shield overlaps the cup may be adjusted according to the height of the spark plug. Preferably the height of the cup is less than the height of the nut member on the spark plug above the receptacleso that the cup does not obstruct access to the nut member.

In a more specific aspect the telescoping edges of the shield and the cup are inclined to the axis of the shield andcup to facilitate inserting the mounting portion of an elbow-shaped hoodmember in the aforementioned opening of the side wall of. the shield.

In a further aspect the cap member is molded of a light, non-metallic, plastic material and coated with a metallic, electrically conducting substance. Preferably the coating covers the entire external surface of the cap, but only partially covers the internal surfaces, so that a shield of low mass is provided with insulating as well as shielding properties.

For the purpose of illustration a typical embodiment of the invention is shown in the drawings in which Fig. l is a sectional View of a spark plug shield installation;

Fig. 2 is an exploded isometric View of a spark plug shielding device;

Fig. 3 is a section of a modified spark plug shield;

Figs. 4 and 5 are isometric views of modifications of a part of the device;

Fig. 6 is a sectional View of another modified shield; and

Fig. 7 is a sectional view of a further modified shielding device.

As shown in the drawings the shielding device comprises a shielding member 1 of suitable electromagnetic shielding properties which is adapted to make a telescoping connection with a metal cup member 3 having similar properties and completely enclose a spark plug P. The spark plug P which has a conventional base B, threaded portion A, hexagonal nut portion N, an insulator I and a terminal or binding post T, is adapted to be screwed in a threaded opening or socket of a cylinder block C. The cup member 3 has an axial opening 4 through which the threaded portion A of the spark plug may pass, the opening 4 being of less diameter than the spark plug base B so that when the plug is inserted in the cylinder block C the base B clamps the cup member 3 against the cylinder block. The shield 1 when fitted over the cup 3 is electrically grounded through the cup to the cylinder block C. The shield and cup member are provided with ventilating and draining openings 6 to prevent the trapping of moisture or saturated air within the shield. To insure a good electrical connection but not necessarily a good mechanical connection finger portions 1? may be bowed outwardly from the wall of the cup member 3a shown in Fig. 4 or slots 21. may be cut in the side walls of the cup 317 and the walls bowed outwardly as shown in Fig. 5. Thereby a yielding fit between the telescoping portions of the shield and cup prevents the electrical connection from being broken by vibration or expansion of the shield.

While the shield as shown in Figs. 1, 2, 3 and 7 is formed of metal, in the embodiment shown in Fig. 6, the shield 1b is molded from a light weight, non-metallic plastic material having heat resisting properties, such as 3 Q mineral filled phenolic plastic. A metallic coating 28 is applied to the outer surface of the plastic shield 1b, and from the outer surface of the plastic shield up the inner surface a sufficient distance to insure electrical contact with the cup member 3, 3a or 3b. The metallic coating is electrically conducting and provides the same electromagnetic shielding as the solid metal shield.

Mounted within the shield 1 is a hood 2 of rubber or elastic rubber substitute material having a mounting portion 7 and a sleeve portion 8. The mounting portion 7 has an axial passage 14 for receiving an ignition cable C having a conducting wire or Wires W. The cable C is covered with a braided wire shield S which may be expanded and fitted over the mounting portion 8 of the hood 2 and soldered or otherwise electrically connected to the shield 1.

An elbow-shaped hood 2 or 2a as shown in Figs. 1, 2, 3, and 7, or a straight hood 2!) as shown in Fig. 6 may be employed. Correspondingly a shield 1, 1a or 1c with a side opening 10, the hood, or a straight shield 1b with an end opening 10a is used. As will be explained hereinafter the hood may be fitted in the shield after manufacture (Figs. 1, 2 and 7), or molded Within the shield (Figs. 3 and 6). The braided wire shield S may be soldered to the shield l as shown in Figs. 1 and 6, or, as shown in Figs. 3 and 7, the shield 1 may be provided with a threaded tubular arm 11 and a screw cap 12 may be used to clamp the end 13 of the braided shield S against the outer end of the arm 11. Electrical connection between the spark plug terminal T and conducting wire W is made by extending the splayed end of the Wire W into the upper end of the bore 5 Where the terminal post T is received as shown in Figs. 1 and 6, or by providing a coiled spring 16 for gripping the terminal post T, the coiled spring having a pointed extension 17 designed to penetrate the cable C and make contact with the wire W as shown in Fig. 3.

Below the bore 5 of the sleeve portion 8 is an enlarged bore adapted to fit over the insulator l of the spark plug 1 and thus provide a seal between the air space within the shield 1 and the terminal post T. As shown in Fig. 1 the upper bore 5 and the lower enlarged bore 15 enclose the spark plug terminal T and the insulator I throughout substantially the entire length of the bores 5 and 15. As shown in Fig. 3 a modified hood 2a is provided with an internal annular rib 26 between the upper bore 5 and the lower bore 15. When the shield is applied to the spark plug the coiled spring clip 16 tightly grips the terminal post T and compresses the annular rib 2-6 against the top of the insulator I, sealing oil the bore 5.

Shown in Fig. 7 is a modified embodiment in which the edges 22 and 23 of the telescoping shield 10 and cup member respectively are formed at an angle to the axis of the shield and cup and the cap member is formed with a shoulder for engaging the edge 23 of the cup member 3a. The shield is of this embodiment is applied to the cup member 3a by removing the screw cap 12. from the threaded arm 11 to relieve the pressure of a sealing ring 13 on the cable C and, by drawing the hood 2a and a portion of the cable C through the forward end of the threaded arm ii so that the shield llc hangs loosely on the cable C. The hood 2a is applied to the end of the spark plug independently of the shield 10. The shield is then telescoped over the cup 3c and simultaneously the cable C and the hook are drawn back into the sleeve of the arm ii. With the hood held firmly in the sleeve the screw cap 12 is then tightened on the sealing ring 18 so that the sea rig ring grips the cable C and holds the hood firmly in position.

Accor ing to the present invention whether an elbowshaped hood 2 or 2a (Figs. 3 and 7) or a straight hood 2b (Fig. 6) is used the mounting portion of the hood is resiliently connected to the shield, and the sleeve portion grips the terminal post T and insulator I of the spark plug so that the shield is mechanically fixed relative to the spark plug by the hood. While the telescoping fit of the hood on the cup provides some support, this fit is primarily an electrical connection, the hood providing a mechanical connection of a resilient, vibration-damping nature not subject to being loosened. In addition the amount by which the shield overlaps the cup is adjustable according to the height of the spark plug.

The resilient connection between the mounting portion of the hood and the shield may be provided in any one of several ways. As shown in Fig. l the sleeve portion 7 is compressed in the opening 10 of the shield. As shown in Figs. 3 and 6 the mounting portion 7 of the hood is molded within the shield. As shown in Fig. 7 the hood 2a is held in a tubular arm 11 by clamping a rubber sealing ring 18 around the ignition cable C with the screw cap 12. In the embodiment of Fig. 7 the shield 1c is further prevented from shifting axially by virtue of its slanted fit with the cup 3a. Any tendency for the shield 10 to twist is limited by the engagement of the edge 23 of the cup 3a with the shoulder 24 formed in the shield. Any of the above described connections may be made with a solid metal shield 1, 1a or 10, or with a metallized plastic shield lb, the plastic shield, however, having a substantial advantage in lower cost of manufacture. Not only does the low mass of the plastic shield 1b reduce to a minimum the tendency of the shield to vibrate loose, but also its low conducting characteristic provides heat and electrical insulation not afforded by a metal shield, and thereby inhibits the collection of condensates within the shield.

An additional advantage of the embodiments of Figs. 1 to 6 resides in limiting the height of the cup member so that it does not extend up to the nut N of the spark plug, and thus leaves the nut unobstructed and accessible to a wrench.

It should be understood that the present disclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents which fall within the scope of the appended claims.

I claim:

1. For shielding a spark plug mounted in a support, a device comprising a metallic cap member for electromagnetically shielding the spark plug, cup means adapted to be fixed relatively to the spark plug support for telescopingly receiving the cap member and electrically connecting the cap member to said support, a hood member of elastic insulating material having a mounting portion and a sleeve portion, said cap member being resiliently attached to the hood at said mounting portion, said sleeve portion having a bore closely fitting the spark plug throughout substantially the entire area of the bore and resiliently gripping the spark plug to hold the cap member thereabout, the telescoping fit of said cap member and cup means being adjustable according to the height of the spark plug, whereby said hood prevents the accumulation of moisture at said post and said cap member is mechanically attached to the spark plug with a vibration-damping elastic connection.

2. For shielding a spark plug having a metallic base and an insulated terminal post extending therefrom, a device comprising a cap having a metallic surface for enclosing and electromagnetically shielding said post, a portion of said cap surface being adapted for electrical connection with the spark plug base, a hood of elastic material mounted within the cap, said hood including a sleeve for tightly gripping the spark plug and a mounting portion resiliently attached to said cap so that said hood forms a resilient mechanical support for the cap on the spark plug, said elastic material being sutficiently stiff to resist loosening of the grip of said sleeve on said post due to vibration so that said hood can hold the cap on the spark plug and maintain said electrical connection without other mechanical connection between the cap and spark plug.

3. Apparatus according to claim 2, characterized in that an inner surface of said cap is adapted slidingly to make said electrical connection and said hood has a pen tion intermediate said sleeve and mounting portion, said intermediate portion deforming to maintain said mechanical connection. in various positions of the hood relative to said spark plug base.

4. For shielding a spark plug mounted in a support, a device comprising a conductor engaging the base of the spark plug and having a surface extending lengthwise of the spark plug, a cap member having a metallic surface for telescoping over and shielding the spark plug and adapted to make a sliding contact with said conductor so as to be in good conducting r lationship therewith in various positions of the cap lengthwise of the spark plug, within said cap a hood of elastic material having a sleeve portion for resiliently telescoping over and gripping the spark plug and a mounting portion resiliently attached to said cap so that said hood forms a resilient mechanical support for the cap on the spark plug, thereby to hold the cap in contact with the conductor in various positions of the cap relative to the spark plug.

5. The device according to claim 4 characterized in that said cap comprises a body of molded, non-metallic, plastic material having a coating of metallic, electrically conducting substance.

6. The device according to claim 5 characterized in that said conductor comprises a cup fitting within said cap and said coating extends from the outside surface of said cap partially over the inside surface of the cap memher to m arse contact with said cup.

Refer-eases fitsd in the file of this patent UNITED STATES PATENTS 1,376,844 Weber May 3, 1921 1,943,739 Nowosielski Jan. 16, 1934 2,301,570 Nowosielski Nov. 10, 1942 2,409,732 Browne et al. Oct. 22, 1946 2,463,924 V an Orden Mar. 8, 1949 2,480,545 Burrell Aug. 30, 1949 

